The present invention relates to the manufacture of semiconductor devices. More particularly, the present invention is directed to methods of substantially uniformly etching oxides that are present on non-homogeneous substrates.
During the manufacture of components for use in semiconductor devices such as capacitors, uniformity of etching can be a problem when performing cleaning operations using an etchant solution. This is especially true where more than one type of material on a substrate is being etched simultaneously, or if the material as deposited or later densified is non-uniform in thickness, density, or composition. For example, when oxide layers are formed by chemical vapor deposition for shallow trench isolation (STI) fill applications, a chemically non-homogeneous film results which may comprise alternating silicon oxide and aluminum oxide layers. When using a conventional oxide etchant solution such as aqueous HF or aqueous NH4F:HF, the exposed aluminum oxide layers tend to etch more slowly than the silicon dioxide layers, resulting in non-uniformities across the substrate surface.
There is also a problem which exists when spin-on-glass (SOG) or spin-on-dielectric (SOD) films are densified. Because the densification process is imperfect, non-uniformities in thickness and/or density often occur in such films as densification tends to be better in open areas than close to walls or other vertical components. Consequently, when conventional oxide etchants are used to clean the film surface, differential etch rates occur which leads to non-uniform etching and results in non-uniformities across the substrate surface.
Accordingly, there is a need in the art for a method of etching a substrate which provides uniform etching when the substrate surface varies in chemical composition, thickness, and/or density.